That is functionally what aluminum (aluminum oxide) and stainless steel (chromium oxide) do. Form an oxide layer which prevents (reduces) further oxidation. Sometimes people are confused about stainless because there is iron present and it can develop some red iron oxides in some alloys.
Local Humidity. There's not really enough water in the air to do more that oxidize the top later.
------------------ King Tut's meteoritic iron dagger shows minimal rust after 3400 years in a dry climate. It's the lower one.
Yes. The welded sculpture is rusty-brown but otherwise fine decades later. OTOH, the stone plinth, surrounding walkways and anything open to run-off rain water is permanently stained a similar brown. There was much flap about a public sculpture at Dalhousie University in Halifax years ago.
Um, well, not in the Arizona desert perhaps. Nova Scotia is very unline the Arizona desert.
Then there is Cor-ten weathering steel used in bridge pier nosings. IIRC it contains some copper, among other things.
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